This invention relates generally to a transmission control apparatus for producing, controlling and directing hydraulic pressure inputs to the clutch, brake and shift mechanism actuators of a transmission for automatically shifting the transmission.
It is well known for an automatic transmission to include a torque converter and a transmission gear mechanism for automatically changing speed stages or gears of the transmission. The torque converter of such a transmission changes the rotational speed of an output shaft of an engine that the transmission is mounted to. The torque converter also transmits the resultant torque to a turbine shaft. The transmission gear mechanism of such a transmission changes the torque speed of the turbine shaft. The gear mechanism also transmits the resultant torque to drive wheels of the vehicle carrying the transmission. A typical transmission gear mechanism includes a planetary gear comprising a sun gear, a ring gear, pinion gears, a carrier, and friction elements. Friction elements typically include components such as clutches and brakes. Clutches are configured to engage a specified gear or carriers and to transmit torques to the engaged gear or carrier. Brakes are configured to alternately lock and release such gears and carriers. Different combinations of friction elements provide different gear ratios for transmitting torque from the engine output shaft to the drive wheels of the vehicle. These different combinations of gears are known as speed stages or simply as xe2x80x9cgearsxe2x80x9d of the transmission. Automatic shifting between combinations of friction elements in an automatic transmission is commonly directed by a transmission controller.
Some transmission controllers include certain of their components in modules that mount on and plug directly into the transmission housings of their host transmissions, i.e., the transmissions that the controllers are to control. Some such modules mount to the host transmission housing by means of fasteners such as bolts or the like. For example, U.S. Pat. No. 5,845,544 issued Dec. 8, 1998 to Huggins et al. discloses a transmission control apparatus including a control module assembly that mounts and plugs into a transmission housing as a one-piece unit. Control module components are housed within a die-cast control module housing that removably mounts to the transmission housing by means of bolts or the like. The control module housing defines a plurality of internal electric and fluid connectors and conduits and is configured such that when the module housing is assembled to a transmission housing, the various conduits defined in the module housing align properly with corresponding conduits defined in the transmission housing.
A printed circuit board disposed in the Huggins et al. module housing includes an electronic controller. A bank of solenoid operated control valves are also disposed within the module housing and are connected to the electronic controller. A position sensor is mounted on an interior of the housing and interacts with a transmission shift shaft of the host transmission in such a way as to detect axial and rotational position changes of the shift shaft. The position sensor is connected to the electronic controller and provides signals to the controllerxe2x80x94signals that indicate the axial and rotational position of the shift shaft. The electronic controller is programmed to control solenoid control valve operation in response to inputs received from sensors such as the position sensor. The Huggins et al. transmission control apparatus is designed to shift an auxiliary portion of a compound manual transmission rather than the main portion of an automatic transmission. The Huggins et al. transmission control uses air rather than hydraulic fluid as its power fluid and requires an external source of pressurized power fluid.
Similar to the Huggins et al. patent, U.S. Pat. No. 4,688,449 issued Aug. 25, 1987 to Harada et al. discloses a hydraulic transmission controller, portions of which are mounted directly to a transmission case of an automatic transmission. The Harada et al. controller selectively engages and disengages clutches and brakes in the transmission thereby effecting gear changes in the transmission over four automatically selected forward speed gears including an overdrive and a manually selected reverse gear. The controller effects the gear changes in accordance with various inputs such as throttle opening of an engine connected to the transmission and the running speed of a vehicle carrying the engine and transmission. The hydraulic controller includes solenoid valves that meter hydraulic fluid to effect the gear changes. The Harada et al. transmission controller cannot, however, shift the transmission it is mounted to without receiving pressurized hydraulic fluid from a separate fluid pump and without inputs from remotely mounted sensors.
A problem inherent in known automatic transmission control systems such as those described above is system variation caused by variations in such factors as pump and solenoid output flow and/or pressure as well as in valve leakage and spring loads. The consequences of system variation in an automatic transmission include reduced fuel economy and drive quality.
What is needed is a hydraulic transmission control apparatus that can automatically shift an automatic transmission without requiring power fluid input from a remote source. What is also needed is such an apparatus that does not require inputs from remotely mounted sensors and that has significantly lower system variation than known systems.
A transmission control apparatus is provided for producing, controlling and directing hydraulic pressure inputs to the clutches, brakes and shift mechanisms of an automatic transmission. The apparatus includes a control module body that mounts on and plugs into an automatic transmission housing as a one-piece unit. Control module components are supported on a module body configured to removably mount to a transmission housing of the transmission, the module body defining a plurality of fluid connectors and conduits. Control valves are disposed on the module body and are configured to meter hydraulic fluid to brake and clutch hydraulic cylinders and/or shift mechanisms in the transmission. Solenoids disposed on the module are connected to respective ones of the control valves and are configured to operate the respective control valves that they are connected to. A controller is connected to the solenoid valves and is configured to control the control valves by operating the solenoids in accordance with inputs received from sensors that detect various factors representing the running state of an associated vehicle drive train. The apparatus also includes a hydraulic oil pump configured to provide pressurized hydraulic oil to the control valves.
Unlike the prior art, the hydraulic oil pump is connected directly to and is supported on the module body. Therefore, a transmission control apparatus constructed according to the invention does not require a remote pressurized source of hydraulic fluid such as a transmission fluid pump that is connected, for example, to the hub of a transmission torque converter.
A transmission control apparatus constructed according to the invention has the additional advantages of greater reliability, easier packaging, lower weight and cost, a simplified logistics and assembly process, and a reduction in system variation achieved by allowing calibration of the control apparatus before the module is delivered to a customer.